An exothermic composition comprises a particulate readily oxidizable metal such as aluminium, magnesium or silicon and an organic fluorine-containing compound, and usually an oxidizing agent for the readily oxidizable metal. The preferred organic fluorine-containing compound is polytetrafluoroethylene. The composition may also contain a binder, a particulate refractory material, refractory fibres and/or organic fibres. The composition may be used in the casting of molten metal, either in particulate form or as a preformed shape such as a sleeve or board, to cover or surround molten metal in the feeder of a casting mould or in the head or head box of an ingot mould.